First Measurement of νe and νμ Interaction Cross Sections at the LHC with FASER’s Emulsion Detector

The first results of the study of high-energy electron neutrino (νₑ) and muon neutrino (νμ) charged-current interactions in the FASERν emulsion-tungsten detector of the FASER experiment at the LHC are presented. A 128.8 kg subset of the FASERν volume was analyzed after exposure to 9.5 fb⁻¹ of sqrt[s]=13.6 TeV pp data. Four (eight) νₑ (νμ) interaction candidate events are observed with a statistical significance of 5.2σ (5.7σ). This is the first direct observation of νₑ interactions at a particle collider and includes the highest-energy νₑ and νμ ever detected from an artificial source. The interaction cross section per nucleon σ/Eν is measured over an energy range of 560-1740 GeV (520-1760 GeV) for νₑ (νμ) to be (1.2-0.7+0.8)×10⁻³⁸ cm² GeV⁻¹ [(0.5±0.2)×10⁻³⁸ cm² GeV⁻¹], consistent with standard model predictions. These are the first measurements of neutrino interaction cross sections in those energy ranges.